To understand women and dating better you really need to know about women's attitude toward casual sex.
Men pursuing casual sex do so far casual sex as an end in itself. Now some women may have casual sex in this way, but they are in a tiny minority. In fact, the idea of indiscriminate sex disgusts most women. To most women, "casual sex" is not casual at all, but part of evaluating a potential long term mate.
It may seem afterward that it was "just a fling", but in the back (or front) of the woman's mind, she is evaluating "where this is going." Put another way, women have sexual affairs with men that (for a time at least) they think may be potential husbands.
With this in mind we can at last explain the "too nice" or "nice guy" problem. Basically, a woman thinks you are "too nice" when you've dated but haven't made any sexual moves on her.
Remember, she's out to find a long-term mate, and part of what a long-term mate has is strong sexual attraction for her. When women complain about men who are "only after one thing", the emphasis is on "only".
They object to the man who is after sex AND NOTHING ELSE. Such a man is sexually indiscriminate and not good prospect as a long-term mate. But here's the point. Neither is a man who is NOT interested in her sexually good long-term mate potential. She wants a man sexually selective; selectively sexually interested in HER.
We can sum it up by saying that:
(i) for women sex and romance go together,
(ii) the "creep" (as women see it) wants sex without romance, and
(iii) the "nice guy" tries to have romance without sex.
So, if you have been called "too nice", it probably isn't some deep personality issue. More probably, it's just a mistaken assumption you've made about women. You've thought that because they complain about men "after only one thing" that they don't want sexual attention in dating.
You've jumped to the mistaken conclusion that if you are sincerely interested in her, you show your respect by not making the moves on her until you've dated quite a few times. That's wrong, you've got to be making moves on the second date at the very latest.
When you make moves on her, it tells her that you are interested in her sexually. But she still doesn't know if you are seeking sex without romance (i.e., a relationship), so she might rebuff your advance.
Here's the key step. She wants to know if you are after sex AND romance, not just sex.
If you get pushy, you don't respect her, so you are not after romance, and you don't REALLY care for her.
If you get angry and hurt, it means (to her) you were expecting casual sex.
If you never try again, it means you didn't really care, you were just after casual sex.
BUT, if you relax, pull back a bit, continue showing her attention and consideration, and then at some later point try again she might be convinced that you are "for real."
So, practically speaking, this means that you should (i) be making moves on her early on in dating, (ii) expect her to resist, and then when she does, respectfully withdraw your advance without resentment and continue being nice to her (you won't be called a "nice guy" for this, she WANTS you to be nice to her, you are "too nice" when you don't make sexual advances, that's all it means), (iii) try again next time, (iv) repeat either she fully rejects you or accepts you.
One last thing, notice this takes TIME. This is what sorts the serious suitors out from the guys after "only one thing" (who give up and move on to the next hopefully "easy lay").
This means that you should (i) really only be going after the girls you really like and are prepared to spend some time on (and perhaps in the end all for nothing), (ii) with these girls you really like, get rid of the idea that putting the moves on them is disrespectful, just do it.