Well, if a friend of yours has a GF, it is only natural for him to not go out to do silly stuff or chase girls. Can you adjust to their new idea of friendship?

You say you were in the hospital for 2 months (for mental health issues?). Sounds like your (old) friends had no idea about this. I understand there is some shame involved here, but if one of the three people still wanted to be your friend, they would have come to visit or reached out to you and they may be irked to learn that you were going through a very hard time, but you didn't tell him.
Yes, also likely that learning about your despression&hospitalization would be a conformation for them that they don't need you in their life anymore.
I wouldn't tell it to new (candidate) friends.

You say that you thought one of your friends could keep up with your 'personal ****'. If you know too many people whose friendship with you involves mainly they talking to you about their problems, it gets annoying and it is not surprising to trade out/abandon a friend.

The healthiest friendships are equal, where both give and take the same amount.