17 year old son has small penis (LONG).

I have no idea where to post this but I could really use some advice. I will try to make this as short as I possibly can, in 2013 my ex-husband and I got a divorce and I got full costudy of our 3 children. (Two boys and our little girl) However, I never tell my children that they can not see or have any contact with their father but they simply choose not to. My ex really doesn't try to be there for them or even try to reach out to them as well. He was always violent and was an abuser. It has been really hard to play that mother/father role and working full time and raise them. But I wouldn't have it any other way. Lately, it has been a real struggle to understand my oldest though, he is 17 years old. I know he is going through changes puberty and such. I noticed he has been really depressed so I finally sat down to talk to him about it, thankfully he was VERY open about everything. He admitted to me that him and his girlfriend of 2 years had sex for the first time a couple weeks ago and they broke up a little after I don't know the reason. But he told me In an argument they had she told him he had a small penis. This was very hard for me to hear as I do not know his body parts now that he is older and there is nothing I can do about that. Not because he is my son but I believe he is a very good looking guy with straight A's, and helps around the house and takes care of his siblings when I have to pick up a few shifts. I was very shocked and quiet the whole time he spoke...but it broke my heart when he told me he KNOWS he has a small one and he wants to do a surgery. Mind you, he had the guts to tell me all this and I feel so flattered for him to be able to trust me and tell me everything and considering that he knows he has a dad out there and he chose to tell me...I was a little disappointed that he had sex so young but there is only so much I could do and encouraged him that if he continues to have sex to at least use protection but right now I think sex is the least of his worries...ladies you can't tell me that size doesn't always matter maybe not to every girl but it does to some. What should I do to comfort him? He is still depressed and hasn't really gone out it's not like him?