yes if you are OK with his continuing the way he is, sex-wise, and are happy with him in other departments.

no if you have any plans for him to change, sex-wise.

also, dissolving a marriage is much harder and much costlier than leaving a boyfriend. There might be some additional financial security that you could get from the legal document, but you would also acquire extra trouble. To compare the financials with and without a marriage, you need to see a professional (a family attorney).

Also, since 50% of marriages end up in divorce, you should already start thinking of how it would be to divorce him, and, if you are a rational individual, the time spent thinking of your future together should equal the time spent thinking about how you would be divorcing him - to match the 50/50. This is not what people normally do when they get married, but I can tell you in hindsight (my problems were not like yours in kind, but still like yours in severity) that it is much more prudent to think hard about how you would be divorcing him. Is his cooperative? Is he vindictive? etc. Many questions to answer before you say "yes".