I'm with you on the straight lines...I can't cut a straight line, I can't draw a straight line and I can't walk a straight line...and I don't drink!!!!
I have trouble with a regular ruler but bought a June Tailor Shape Cut ruler and love it so much, I bought her Exact Eighths and Perfect Half-Square & Quarter Square Triangles rulers. Once everything is lined up, I can make several cuts and the fabric and ruler both behave better for me. She also has a Quarter Cut ruler and, when I find it either on sale or where I can use a percent off coupon, I plan to invest in it as well.
Once I read on this board about starching before cutting fabric, it made the cutting and the sewing much easier.
I put off trying half square triangles for a long time because they intimidated me. You are much braver than me!!!
You are very wise to step away when you get frustrated so you keep it enjoyable. Don't give up...it will get easier!