Here are my two cents, which are perhaps more valuable to you or are maybe worth nothing.
If you have different personalities around different persons, what you are doing is attempting to tailor a persona for each individual. Everyone in society does this to some degree, except the most severely autistic or obnoxious among us. For social interaction to work, we must be willing to meet those whom we engage with at some common point between where you are coming from, and where the other person stands. People who are rude and inconsiderate are generally disliked because they won't even meet close to halfway. And many great conversationalists are great because they recognize many unspoken aspects of an interaction, and are willing to go beyond halfway and put a little extra effort into building a good rapport.
It sounds to me like on that spectrum between you and the other person, you're going well over to their end to meet them. But if you are beginning to doubt who you are and are feeling alone, perhaps the problem is that you're going too far. You're expending all of your energy meeting their needs, and you're not meeting your own. If you want to change this, you have to be willing to let yourself be honest at times and express what you think and feel, instead of what you think the other person wants to hear. Not only is it exhausting to please others all the time, it leaves you feeling isolated since you never actually connect—only your personas do.