Falling pregnant is more than just introducing sperm & eggs - alot more.

1) have either of them been tested to assess fertility?? Low sperm count or none, non-functioning ovaries? Etc. Also have other health issues which can affect ability to fall pregnant/produce sperm that do their part been assessed -- eg weight, general health, hormone levels, blood pressure, smoking, drinking to excess??

2) as from what you said these 2 are not a couple there may be some stress/lack of emotional comfort involved (regardless of both having agreed & being really mature about it etc) which could reduce the chancess of success.

3) many women ovulate mid cycle but just as many ovulate at different times of the month, including ovulating more than once, or at varying times (called a floating ovulation) - so if they only have sex at the "normally" optimum time of month & the girl is not ovulating then well>>>> no success is likely.

4) if either is not fully fit (even a cold) this may impact on the result.

5) many "straight" couples find that a relaxing night out a couple of wines, some "romance" & well you can get lucky, as this situation is different perhaps you could still suggest that your g/f & the guy could go to dinner & a movie & listen to music, chat, relax & then have sex, rather than it just being a business, or necessary act.

6) it was unclear from your post as to whether the guy knows what's going on - if this is the case then your g/f may be feeling guilt & so stressed & this would decrease her chances of falling pregnant.

7) as to how long people normally wait before getting checked out - that depends on whether the above have been checked/tried, whether any emotional issues need to be addressed (due to them causing stress & so reducing chances of conception) & also whether either party has a family history of problems conceiving or of miscarriages.

if either party hsa a family history which would indicate that there might be problems then most people would go after about 6 to 12 months - assuming that all the other points above have been ruled out or resolved.

9) but it often takes people 2-3 years of trying before they fall pregnant - if you are feeling jealous(?) & your g/f is picking up on this then it won't help.

Good luck