Does anyone else always feel like the extra friend?

Lately I’ve been feeling very left out of things with my group of friends. It seems some way or another different people bonded and I was suddenly left all alone. Three of my friends recently got boyfriends so they’ve all been spending time together talking about them and my two other friends just have more opportunities to talk. I really thought me and my friend were bonding but the other day she chose to sit with my other friend on the bus meaning I had to sit alone in a seat. They both proceeded to put earbuds in and completely ignore me. For some reason I’ve always been the odd friend out and it’s just hurtful and lonely. I also know it’s partly my fault because I decline a lot of offers to go out. So I take full responsibility for my situation but that still doesn’t make it any less hurtful. Usually I say no because I know that I’m going to end up walking behind them on the sidewalk or sitting on one side of the booth alone. It just seems like even when I make an effort to bond it never works. Please tell me I’m not the only one in this position. If there is anyone also in my spot or has been how did you handle it?