Number one. Almost all married people, men and women, continue to masturbate.
When a married person masturbates it is not a sign that he/she is unhappily married or not satisfied with the sexual relationship within the marriage. In fact, surveys show that people who are very happily married and satisfied with their sexual relationship still continue to masturbate.
It seems that the sexual relationship that we establish with ourselves as individuals needs to continue even after we form a union with another person, much the same way that a person continues to take care of him/herself and grow even after forming a relationship with another.
The fact that you take his masturbation as a person insult is worrisome to me. You are using his behavior as proof that you aren't attractive enough.
When a person has a low self-esteem it is common to interpret all kinds of situations as further proof of how unworthy or worthless he/she is. The result is a lowering of the self-esteem.
Don't stick your ego where it doesn't belong. His behavior is normal and is in no way a reflection on you. If you need help with this issue, then, by all means, go and talk with a therapist.