As frustrating as it is right now, in a few days, weeks, months, etc, everything will change again. Right now, he's at a prime growth spurt age, and he'll go through another at 3-4 months and again possibly around 6mo. THEN, you get to have the interrupted sleep of him learning new things like sitting, crawling, etc. Parents have to go with the flow, but it never hurts to try to have some sort of routine.
At 9wks, your son is WAY to young for sleep training. It's good that you're starting a routine with him, but unrealistic to expect him to go to sleep when YOU desire. At 9wks, both my kids were still on their "newborn" schedule of days and nights mixed up. My daughter didn't go down for her longest sleep until about 1am, and my son about 2am. Granted, I didn't have to work or really get up for any particular reason. However, I did notice with my daughter that having a toddler in the house already (who had his own ideas about what time to wake up hehe) helped with getting her schedule flipped around. My daughter is now 8mo and goes to bed anywhere between 8:30 & 10 and sleeps an average of 11 hours with 1-2 night feedings.
The way I gauge bedtime with her (and my son when he was younger) is to pay attention to her nap time. I know that she's ready for bed about 4-5 hours after she wakes from her afternoon nap. With your son being so young, I'd say to pay more attention to his behavior. His fussy time in the evening could be just that... his fussy time. Many infants have a time of day - usually in the evening - that they are fussy for no seemingly apparent reason. Doctors call it colic, and it usually disappears around 3mo.
Another thing I've learned is there are 3 things you absolutely canNOT force a baby to do: eat, sleep, and poop. If he cries when you try to put him to sleep, try letting him stay up. It may be less stressful for you all to go more on his schedule. Or you could go the other way and start bedtime a little earlier. Right now, the important thing is to enjoy your son while he's so little! My success the 2nd time around was in not trying to force things. If she didn't fall asleep easily, I let her stay up 15-30 minutes longer. Sometimes, this extra time was accompanied by some hard tears and prayers for her to just go to sleep!!! Being a parent is definitely the most challenging job I've ever had, but it's also the most rewarding when you see this happy baby!
(FYI, there is NOTHING wrong with nursing your baby to sleep!! Especially at 9wks!!! I still nurse my 8mo to sleep for both naps and bedtime, and she sleeps just fine!)