Why did he lie?

I went to the hospital to get the implant, my boyfriend said he would come with me, it is for his benefit too and I needed someone to come in case I didn't feel safe to drive afterwards. The appointment was booked for weeks.

The day before the appointment his friend asked him to go to Wales with him at the same time. Instead of saying he was coming with me, he told his friend he had a hospital appointment because apparently his friend wouldn't see my appointment as an appropriate excuse! His friend then said he'd take him to the hospital and they'd go to wales after, but obviously it was my appointment so he just told his friend I was going with him.

Anyway, he did come with me, but went to Wales straight after. Why couldn't he just tell his friend the truth and stand up for the fact he thought coming with me was more important?

He's let me down for his friend. For example he made me drive him home even though we'd arranged to spend the day together so he could go with his friend to pick up some cannabis and he asked him to last minute. I really didn't feel like taking him but I did. The he expected me to go round straight after.

What are your opinions on this? Should he have lied?