ADHD and OCD

Just found this site and I am horrified at the stories of lying, cheating and infidelity.  I have dated a man for over a year but recently found some activity on his computer like you all - hookup sites, texting, etc. Of course denying it was nothing or "just looking."  Still don't believe that. Upon the recent discovery, he agreed to go to counseling for his ADHD.  He is early 40's, never married, no real long term relationships and wants to find out why he can't seem to stay in a relationship, why he loses focus so easily.  He is very organized, takes care of things, not lazy, works out, good job, (probably his ocd) has a good heart, is good to me, but has a hard time opening up emotionally (might be adhd might be childhood stuff) and expressing his feelings.  I can handle the not opening up part but it's the seeking out other women part that frightens me.  He says he loves me and wants to make this to work  and have a lot in common, so it doesn't appear he's looking to find another woman for long term.  I do want to give him a chance but after reading this site, I am so scared.   Is getting counseling and possibly on meds early on in a relationship a sign of hope or willingness - we are not married - or are these people just doomed.  If it was just the lack of opening up that would be one thing but the hookup sites???  Can the ADHD/OCD guy ever kick the need for stimulation in this area and really be faithful?  He says he doesn't want to be alone the rest of his life and wants to figure out how to prevent that.  He does seem like the type of person to better himself but his "just looking" went on for a while before I found out.  and the texting after about 10 months into our relationship.  he did check out other women frequently but has sense stopped doing that while with me.  Are these guys just not able to control themselves in this area?  I don't want to move forward get married and discover I'm living with a cheating lying monster.