Am I being childish?

guy I am currently committed to revealed that he occasionally chats with his ex. An ex he cheated on me with in the beginning after being together for 5 months, due to a nasty argument. He confessed to me, stating that I deserve better and left me for her. We didn't talk for months after that, he left voicemails stating that he regretted it, stating that she helped him financially at a time where his addiction was getting out of hand. An addiction I wasn't aware of. He continued on stating that our connection was strong and more mature, and was ready to get help and grow up. They lasted for a season, then broke up. Months later we eventually chatted again, and the feelings came back, so we decided to give it another shot and take it slow. Then found out that he is friends with her on facebook and "chat it up" every now and again. It worries me. First off, I am not friends with any exes and never felt it was smart to be friends with exes. I have had this issue in past relationships before. Am I childish for this? I ask because I know people that are friends with exes, and get along in life in their current relationships. As for me, i simply don't get it. I view exes as failed attempts to trust and commitment, that being said in my opinion keeping them as friends is a sad reminder and brings up too many bad memories. Am I silly, should i be worried? Anyway we argued about it and he swore that she is just a friend and is not interested in him "like that" anymore and vice versa. He swears that he only wants me. Generally i am not a jealous person but i feel like this is different because they had a "drug induced" relationship and from what i heard people who date each other and do drugs together have a weird bond. As stupid as this sounds, I sort of wish he chose me to get high with instead of her, because now i feel like she will always have that memory with him. Am i overanalyzing? Meanwhile its only been a year since we been together and i feel like maybe we just have to stick it out a little longer before i jump to conclusions and run (like i usually do) :( i just love him so much but i love myself too and am not trying to get hurt again.

No, you are not childish. You can choose to do what you think is right, by you, since we all have one life in this world. No one is allowed to judge our decisions. Not all exes remain friends, sometimes it works and sometimes it does not. Your maturity is not based on being friends with your ex. I completely understand you wanting to have done drugs with him instead of him. No, you are not overanalyzing. You wanted things to be special with him. Wish you the best.