I think the most basic meaning of যেন is "as if", e.g.
1a. আমার মনে হল যেন সমুদ্রের ধারে বসে আছি। = I felt as if I was sitting at the seaside.
or as in Tagore's poem:
1b. "মনে করো যেন বিদেশ ঘুরে
মা-কে নিয়ে যাচ্ছি অনেক দূরে"
= "Imagine that (=as if) I am taking Mom far away through the foreign lands..."
1c. কি সুন্দর, ঠিক যেন সুইৎজারল্যাণ্ড! = How beautiful, just like / as if Switzerland!
One very interesting and probably difficult-to-learn extension of this meaning is the use of যেন as an "evidentiality marker" expressing that the information contained in the sentence comes from uncertain recollection. It may have evolved as an ellipsis of "মনে হল যেন" or some such expression:
2a. তোমাকে যেন কাল বাজারে দেখলাম! = (I think) I saw you in the market yesterday!
In questions, this implies "I can't recall exactly":
2b. কী যেন নামটা ওর? = What's his/her name? (I can't recall it, but I knew it before!)
Then comes the other important use where যেন + simple present has a similar meaning as an imperative. I am not sure, but it seems to be limited to 1st and 3rd persons only, where this is also the only way of forming imperative negative. This যেন often imparts a sense of reminding, warning, etc. with empathy making the request or command less direct:
3a. ঠাকুর আমাদের ভালো রাখুন! = ঠাকুর যেন আমাদের ভালো রাখেন! = May God keep us well.
3b. এ কাজ যেন আমরা কখনও না করি! = Let us (be warned that we) never do this
3c. দেখো, টাকাটা যেন না হারায়! = Be careful that the money is not lost.
Note that the "na" here usually precedes the verb, but not necessarily. This negative construct can be used also in the 2nd person when empathy is to be expressed, where the verb can either be in na+simple present (as above) or the normal 2nd person negative imperative, i.e. future imperative + na:
3d. দেখো, টাকাটা যেন না হারাও! = দেখো, টাকাটা যেন হারিও না! = Be careful that you don't lose the money.
And then there is the যেন of your example, where there is a cause-and-effect relation between the two clauses. There it means "so that", but, in my opinion, a less ambiguous alternative here would be যাতে.
