You are still a young woman who has plenty of time to make a decision and to learn from it. First, if I were you, I wouldn't get back to the first guy because 4-5 times on and off can prove that your relationship with him is unstable at all. You said he is going better and better but it doesn't mean that he will be the best one for you, right?
About the early middle age guy, he impressed you at first sight and you already checked that he is surely single man. But do you exactly know that why he is still single at his age? As you said "I'm not sure that we would have a happy marriage life", I agree that you need to know more and more about him, and moreover, I think text and call can prove nothing. Thus let it be a matter of time and give yourself a chance to meet some other guys and learn them.
About "Skin ship", sometimes I also need it to cheer me up as well. Anyway if your "Skin ship" is not limited only to "Sex", I strongly believe that you can get it from someone else not only the one you are dating with as I am deriving now in my life. But if it is about "Sex", I have no idea and I am not in the point that I can provide you any good suggestion because I know very few about you.
Although boyfriend is something very important to have, but you won't be death without right? Sometimes best friend is also very important to have too.