Complicated question because everyone's situation is different. Realistically I would need a lot of more information to go on. If you'd like to tell me more about it, feel free to contact me and I'll try to give you better advice, but here goes.
The reason's I've "lost" feelings for a girl in the past:
- My feelings were not as genuine to begin with as I thought. New things are exciting, especially relationships. There are all of the sexual thoughts and the desire to feel wanted/appreciated. Sometimes when that initial lure wears off it just isn't what you thought it was.
- I did not feel like my feelings were reciprocated. My girlfriend never showed me her affection well enough and I felt I was in a 1 way relationship. There are many, many things that can make someone feel this way.
- I didn't really, I just got interested in other things too or the girl perceived that I had lost feelings even though I had not.
All 3 of these, and other cases, have different solutions clearly. However, I can give you two universal pieces of advice. COMMUNICATE! Communication is the number one way of solving problems hands down and it isn't close. For example, you can easily find out and correct #2&3 if you just ask your BF and learn that this is the issue. Young girls struggle with this especially. People don't know what you want or what is bothering you unless you tell them, so just tell them. The other piece of advice... There are really only two types of relationships, shallow ones where you really just want to bang or get comfort and long term relationships. If your relationship is struggling at all in the first few years, realistically it's doomed and you should let it go. If he's falling out of love with you right now, just imagine after you're married for 20 years and there is no spark in your relationship at all, it's going to be way, way worse. Stop trying to hold on to bad relationships and force them to work. The whole point of dating is to find the relationship that works for you effortlessly.
Like I said, if you want to talk more, hmu.