One researcher at Marquette University just completed a longitudinal study of behavior within romantic relationships. One hundred thirty-seven non-married couples (46 male-male, 46 female-female, and 45 male-female) involved in relationships six months or less participated.
Not surprisingly, relationship satisfaction was related to the total reported relationship benefits, and having more positive relationship aspects than negative aspects. So basically, if you can identify more plusses than minuses in your relationship, you're probably fairly satisfied.
Interestingly, though, relationship satisfaction was related to the partner's use of substances (drugs/alcohol). If your partner doesn't abuse substances, your relationship might become more satisfying.
Sexual satisfaction was related to differences between themselves and their partner being complementary, thinking of their significant others as a potential long-term partner, communication problems, and partner substance use.
On our home page (https://www.gaycouplesinstitute.org/), we have a quiz if you would like to measure your relationship satisfaction. You can schedule a phone appointment to receive your results, which are usually quite amazing. Top score is 151.
Simons, Gregory, Dissertation Abstracts International: Section B: The Sciences and Engineering, Vol 68 (8-B), 2008. pp. 5593.