Division bench of Supreme Court held that,

From Para 306,

26. Section 306 refers to abetment of suicide. It says that if any person commits suicide, whoever abets the commission of such suicide, shall be punished with imprisonment for a term which may extend to 10 years and shall also be liable to fine. The action for committing suicide is also on account of mental disturbance caused by mental and physical cruelty. To constitute an offence under Section 306, the prosecution has to establish that a person has committed suicide and the suicide was abetted by the accused. Prosecution has to establish beyond reasonable doubt that the deceased committed suicide and the accused abetted the commission of suicide. But for the alleged extra marital relationship, which if proved, could be illegal and immoral, nothing has been brought out by the prosecution to show that the accused had provoked, incited or induced the wife to commit suicide.

From Para 28, exoneration of husband,

28. Suicide note completely exonerates A-1, which states that he was not responsible for death of the deceased. On the other hand, the deceased described herself as extremely selfish, egoist and, therefore, not a match for A-1. She entertained the belief that her husband A-1 was in love with A-2 and wanted to marry A-2. Note states it was for their happiness she had decided to end her life. She also wanted to have the marriage of A-1 and A-2 solemnized with pomp and gaiety. On reading the suicide note, one can infer that the deceased was so possessive of her husband, and was always under an emotional stress that she might lose her husband. Too much of possessiveness could also lead to serious emotional stress, over and above the fact that she had one abortion and her daughter died after few days of birth. No evidence is forthcoming in this case to show that A-2 ever evinced any interest to marry A-1. On the other hand, during the subsistence of the alleged relationship, A-2 herself got married.

Citations : [2013 CRLJ SC 44482013 AIOL 5932013 CRIMES SC 4 2952013 CRIMES SC 4 1102013 SCC 10 482013 AIR SC 52192013 RCR CRIMINAL SC 4 2712013 SLT 7 7062014 AIR SC 3312013 SCALE 11 1982013 JT 12 3572013 SUPREME 6 3662014 JLJR SC 1 3902013 SCC CRI 3 8012013 SCC CIV 4 6162013 SCC ONLINE SC 8142013 AIC 130 292013 CRILJ 44482014 PLJR 1 5112013 BOMCR CRI 4 5222013 UC 3 19352013 DMC 3 2452014 ALT CRL AP 1 2582013 ALD CRI 2 7552013 MLJ CRI 3 7002013 OLR 2 8672013 KHC 3 8102013 AD SC 10 452013 ABR 6 1792014 SCJ 1 5262013 RCR CRIMINAL 4 2712014 JLJR 1 3902013 CRI LJ 44482013 MLJ CRL 3 7002013 AIR SCW 5219

Other Sources :

https://indiankanoon.org/doc/170814796/

https://www.casemine.com/judgement/in/5609af2de4b0149711415bb9

https://www.scconline.com/blog/post/2015/02/25/husband-s-extra-marital-relationship-does-not-amount-to-cruelty/