Clarity is needed and should be used.
You strike me as a person who is 'old fashion' and has certain needs (not mere wants) in order to be comfortable in a relationship. What you need to do is figure out a nice way of telling potential suitors what those 'needs' are.
I am an old fashion guy. I have needs - those needs means that I make guys wait before we slip into bed.
I would tell guys who I met that I had a few ground rules.
1. I'm looking for a long term monogamous relationship, I don't do casual sex.
2. I prefer to wait a while, date and see what other common interests we have before jumping into bed.
3. We can talk about sex, limits and roles, but do not expect that to lead to bed.... immediately.
Yes, many potential would be suitors walked before I finished line one.
I get these out on the first date. Sometimes at the first meeting, especially those guys who walked up with drink in hand for me and gave me some odd pick-up line, weed out those weeds as soon as they crop up - saves lots of time and hassle later on.
I make certain that we are on the same page. No false hopes, no misunderstandings. Yes, many first dates will end right there, but these guys are not wanting what you need.
Better to know on the first date than 2-5 dates later when you 'drop the bomb'. He most likely assumed you were just playing hard to get, or he just figures that you are not that into him and he goes wandering off to the next tight hole....
I used to think that talking about sex was a huge social no-no. It isn't. Well it can be if you are in the middle of a posh restaurant ticking off the positions you will do. There is a right place and a right time to discuss sexual matters.
Gay men are usually more open to talking about sex, in privacy its ok to discuss what it is you like to do and not do. In fact when it comes to potential relationship material its nice to know BEFORE you invest hundreds of dollars in food, wine and dance that the guy you are wanting to have a relationship with is a top/bottom, into S&M or not, into golden showers, scat, latex, fisting, etc... After all if you are not into being tied up and having a fist inserted up your ass you sure don't want to find out he is into that when he has you tied down....
"because I think I'm a bottom"
I take it to mean you haven't had sex with another guy. Well you need to be honest about this and let potential suitors know. Did this guy know that you haven't had sex with a guy before? If yes then he just wasn't interested, if no then he he didn't know, thus he figured you were a prude. Had he known he may have been far more receptive to taking things slowly understanding that this is all new for you.
There is also this whole world of experiences that you haven't tried, so this is going to make the whole 'lets talk about what you like (in bed)' conversation a bit tricky because you lack experiences.
Yeah sure, you can pretty much know if the idea of a fist up the butt is a 'hot' idear or not so can be certain if the idea absolutely terrifies you, that you will not be into it. But other things like 'Am I a top, am I a bottom, am I versatile?' become tricky. The idea of a dick up the ass is not the same thing as having one up the ass. Many guys love the idea, they do not like the experience.
Set reasonable boundaries and goals - sit down and right up a list of the 5 most important things you need for a relationship, then select the three most important and make certain that somewhere in that first date you tell the guy 'these are the three must haves'. If you don't, you will be wasting a lot of your time, their time and most likely will not get what it is you are looking for.