My last two cycles lasted 52 and then 42 days. i had sex 10 days after the start of my new cycle. how likely is it that i would become pregnant?

Not likely: You likely did not ovulate 10 days after the first day of your last period since your cycles are so long. Ovulation typically occurs 14 days before the first day of period. Ovulation occurs 14 days after the first day of period only if your cycle is regular 28 days (I hope this makes sense). Keep track of your basal body temp or use ovulation kit to estimate ovulation.