Hi Alice, I'd like to help you with your question.
It sounds like you have a few things going on here. One, you married young and so took on responsibility early on in adulthood. Two, you married someone who you wanted to care for you (and he does in a certain way) but that ended up needing you more than you need him.
As you describe your husband, he does sound like a nice man who cares for you. But at the same time, he is needy. You mentioned that he did not stand up to the men in bars asking you for your number nor does he have courage. You also mentioned he wants you to do for him all the time and that you cannot hurt his feelings in any way. From this description it sounds like he has a very poor self esteem. Anyone who does not stand up for themselves or gets their feelings hurt easily lacks the self esteem to feel they are worthy to ask for what they need. He could also have a dependent personality as well, but at this point it sounds like a low self esteem issue.
From what you said about how you feel, it sounds like you have built up some resentment about the situation. You took responsibility early on in the relationship to support the two of you and you continue to be responsible for your husband's fragile ego. That is a lot of burden. Meanwhile, you feel you are not getting your needs met in the relationship and now desire to go outside of it to seek what you feel you need.
You can go outside your marriage to get what you need, but the damage to your relationship would be great. Even if you did not intend to cheat, you may be tempted beyond your limits. Or your husband could do something one day to trigger your boundaries. And if you did cheat, you would ruin the trust between you and your husband.
Try talking to him about counseling. You both need to talk this issue through to see if you can work it out, before you take any other action. To find a therapist, talk to your doctor about a referral. Or contact your local United Way about low cost/no cost therapy in your area.
Also, try talking to your husband about improving his self esteem. There are many resources on line and through books that can help him. Here are some:
Self-Esteem: A Proven Program of Cognitive Techniques for Assessing, Improving, and Maintaining Your Self-Esteem by Patrick Fanning and Matthew McKay PhD
The Self-Esteem Workbook by Glenn R. Schiraldi
Start here and see where it takes you. With just some therapy and self help, you could both improve your relationship to the point you are both happy.
I hope this has helped you,