Lyndzey,
okay, hun you sound a lil freaked..So just take a big long deep breath...
Now, since you've probably been stressing about being pregnant ever since the partial cum in you incident--stress might just be the probaly as to why you're late.
How many days late are you? I know i've been late up to 2 weeks with being pregnant, just because I was so stressed about being pregz.
But...Since you haven't been using any form of b/c, you could very well be preg..Not to freak you out....But thats the risk you take. If not preg from him partially cumming in you, it could be from pre-cum.
Either way, you should take a home preg test. That way you'll know where you stand. If its negative then you can just relax and wait for your period to come..If it doesn't come, then test again in week or so, or get a blood test done.
If it come back positive, you'll have some pretty big choices to make in the next couple months as to what you're going to do about it.
No matter how it come out, we'll all be here to support ya. Don't be afraid to ask questions.
Best of luck hun