Hey OP, a pretty similar thing happened to me last year. Sorry if it's too long but I'm not good at summarizing.
I had only two friends that I really opened up to and viceversa, and I decided to make them meet and talk with each other, since they didn't really have any other friends.
He fell in love with her, she kind of rolled with it and I started going out both and kind of keeping their conversations going when it would stop; I was very happy that something started between them.
In the meanwhile I started having some problems, the bigger being my girlfriend-at-the-time's attempted suicide; she failed but the antidepressants she had to took after that molded her personality and she basically became her own shadow. I didn't know how to handle that (+ other minor but stressful problems I had outside that) because I realized I didn't love her anymore but I really had an hard time deciding whether to leave her or not and felt like shit for thinking about it (didn't want her to overreact neither...) and I needed help, but my two friends were really into what was blossoming between them, so the help they gave me was kind of rushed off and they weren't really worried or interested.
Once they got in a relationship he started getting really jealous as I was her best friend and also a male, while she got so invested in the relationship that she spent her time texting to him everytime we went out. I basically lost them and spent the summer alone; I found a way to get out of that problem of mine but I was still feeling really down and was still stressed out due to personal/family problems and I had suicidal thoughts more often than I'd like to admit.
Things started to change towards the end of the summer, when I started volunteering at a summercamp, and here I met two girls that soon became my best friends and we started doing lots of activities together and that really cheered me up.