I have a question that I would like to see if you can answer. I have been reading many of the questions you have answered, and it has raised more questions. I was wondering if it would be sinful if my girlfriend was to send me pictures of her in nothing but her bra and underwear as long as it was not for lustful reasons. Also, would it be sinful if I was to rub her breasts and nothing else, since she can not really feel when they are touched? Nether of us get aroused by it. We have just recently found out that getting each other to orgasm or ejaculating is a sin, so we have decided to stop. If you can answer my questions that would be great. I have looked everywhere and can't find a answer to my first question.
Your question isn't consistent, so I'm having a hard time figuring out where you are coming from. I don't know if you are using incorrect definitions for words like lust and aroused, or if you are trying hard to pretend that things less than they are.
Let's take your first example, why would a girl send a boy pictures of herself in undergarments? You said it isn't for lustful reasons. If that were true, then why not send pictures of herself fully clothed? While you might have gotten so used to seeing her wearing little that your penis no longer gets instantly erect, it doesn't mean you aren't aroused.
One of the problems with sin is that when a person is repeatedly exposed to something that is wrong, it doesn't bother them like it would at the beginning. It is like forming a callous, or as Paul describes it, "having their own conscience seared with a hot iron" (I Timothy 4:1-2). My point is that your lack of reaction isn't necessarily a good way to measure whether something is right. A strong reaction on your part could be a warning that things are going too far and too quickly, but a lack isn't permission to go further.
So let's judge this situation in a different way. Would you say she was modestly dressed? Would it bother you or her if your parents saw those pictures? Would she object if those pictures were framed and placed in your living room? "In like manner also, that the women adorn themselves in modest apparel, with propriety and moderation, not with braided hair or gold or pearls or costly clothing, but, which is proper for women professing godliness, with good works" (I Timothy 2:9-10). I suspect that your girlfriend wants those pictures to remain private. That tells me that she understands that the pictures are meant to be provocative and arousing -- they aren't modest.
This is why I said the question wasn't consistent. You claim it isn't for the purpose of lust, yet it clear is done with the motivation of stirring lust.
Your second example is the same. Why do you want to rub her breasts, if it truly does nothing for either of you? Again, there is the possibility of becoming calloused to the effect it causes, so this isn't a good way to measure correctness. So suppose you walked in a room and saw a young man rubbing your girlfriend's breasts, what would you conclude? Would you accept their answer that it was nothing because both of them denied to be aroused by it?
By changing the situation around, suddenly the excuses you give yourself aren't the ones you would accept from someone else.
A woman's breasts has a large number of nerves which are connected to her sexual response. To say she doesn't feel all that much tells me that someone isn't being fully honest.
God teaches us that sex belongs in marriages. There are very good reasons behind that law because casual sex can lead to all sorts of long term harm. "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman. Nevertheless, because of sexual immorality, let each man have his own wife, and let each woman have her own husband. Let the husband render to his wife the affection due her, and likewise also the wife to her husband" (I Corinthians 7:1-3). The problem you are running into is where to draw the line between acceptable and unacceptable behavior. But you are approaching the problem backwards. What you should be looking for are ways to be with each other that does not tempt you to get closer to having sex. "Therefore let us not judge one another anymore, but rather resolve this, not to put a stumbling block or a cause to fall in our brother's way" (Romans 14:13). When two Christians love each other, they ought not want the one they love to sin, so they behave in ways that minimize the temptation to sin.
What you are going to find is that if this relationship of yours is true love, then your restraint is going to increase your desire for each other. But unlike the sexual touching that you had been involved in, this desire won't leave you feeling dirty and ashamed of what you did. And instead of everything focusing on sexual matters, you are going to make connection to each other in so many ways that you will truly become each others' best friends. And the day of your wedding comes, that night will set off fireworks that you could not imagine before. Love is truly worth the wait.
"I charge you, O daughters of Jerusalem, by the gazelles or by the does of the field, do not stir up nor awaken love until it pleases" (Song of Solomon 2:7).